The human body is a complex and intricate system where various organs work in harmony to maintain optimal health. Among these organs, the thyroid gland plays a crucial role in regulating metabolism, energy production, and overall hormonal balance. However, like any other system, the thyroid can be susceptible to dysfunction and disorders.
Thyroid autoimmunity is a prevalent condition that affects millions of individuals worldwide. It occurs when the immune system mistakenly identifies components of the thyroid gland as foreign and launches an attack against them.
How the Immune System Affects the Thyroid Gland
The immune system’s job is to detect and destroy bacteria or viruses in the blood. White blood cells, which fight infections, make proteins or antibodies that detect these invaders. These markers tag the invaders and then are used by other components of the immune system to destroy or rid the body of these invaders.
Once a significant number of thyroid cells are destroyed, there is little or no thyroid hormone production. Unfortunately, we don’t know why the immune system starts to attack the thyroid gland.
Hashimoto’s Hypothyroidism
Hashimoto’s hypothyroidism is an autoimmune disorder where the thyroid cells are attacked and destroyed by our own immune system. It is a very common cause of hypothyroidism. In Hashimoto’s hypothyroidism, the immune system misfires and treats parts of the thyroid gland as an invader.
If your thyroid hormone levels are consistent with hypothyroidism or an underactive thyroid gland, your provider may do tests to look for Hashimoto’s.
Children With Hashimoto’s
Children with hashimoto’s hypothyroidism are also at risk for developing other autoimmune diseases such as celiac disease and more rarely, autoimmune adrenal disease or Addison’s. In addition, children with type 1 diabetes or Turner syndrome are at a higher risk than their peers for developing hashimoto’s hypothyroidism.
A pediatric endocrinologist may be helpful in evaluating and treating children with hashimoto’s hypothyroidism.
Anti Thyroid Peroxidase Antibody (TPO Ab) vs Anti Thyroglobulin Antibody (AntiTg Ab)
Two of the most common autoantibodies associated with thyroid autoimmunity are Anti Thyroid Peroxidase Antibody (TPO Ab) and Anti Thyroglobulin Antibody (antiTg Ab). There are blood tests that can be performed to detect thyroid antibodies in Hashimoto’s. Once antibodies are detected in Hashimoto’s disease, these tests are not necessary to repeat.
Both thyroid peroxidase and thyroglobulin are found in the thyroid gland only and play a role in thyroid hormone production. Most providers will evaluate an individual for autoimmune thyroid disease using only anti-TPO Ab.
Targeted Antigens
TPO Ab primarily targets an enzyme called thyroid peroxidase, which is essential for the synthesis of thyroid hormones. This antibody interferes with the enzyme’s activity, impairing the production of thyroid hormones and leading to hypothyroidism.
In contrast, AntiTg Ab targets thyroglobulin, a protein that serves as a precursor for thyroid hormone synthesis. When AntiTg Ab levels are elevated, it indicates an immune response against thyroglobulin, potentially leading to thyroid inflammation and dysfunction.
Anti-Tg Ab are often obtained in individuals with history of thyroid cancer who have had their thyroid gland surgically removed. It can be an important test in thyroid cancer surveillance after treatment.
Note, if you have a positive antibody that does not mean you will develop hypothyroidism.
Clinical Associations
TPO Ab is strongly associated with Hashimoto’s thyroiditis, which is the most common cause of hypothyroidism characterized by chronic inflammation of the thyroid gland. It is also frequently found in individuals with other autoimmune conditions like rheumatoid arthritis or type 1 diabetes.
A significant number of individuals have positive antibodies and don’t need to be on medication for hypothyroidism. A few individuals may have autoimmune thyroid disease without detectable antibodies. This may be due to a reduced amount of antibody production in the body or a limitation of the assay.
Conversely, elevated levels of AntiTg Ab are commonly observed in Hashimoto’s thyroiditis, as well as in Graves’ disease, an autoimmune disorder leading to hyperthyroidism. There are also thyroid receptor antibodies found in Graves’ disease. Obtaining the levels of these antibodies can aid in diagnosing and differentiating between various autoimmune thyroid conditions.
Diagnostic Significance
TPO Ab and AntiTg Ab play a crucial role in the diagnosis of autoimmune thyroid diseases. Measuring their levels through blood tests helps identify individuals at risk or those already affected by these conditions.
Elevated levels of TPO Ab and AntiTg Ab are indicative of autoimmune thyroiditis. Once again, it’s important to note that the presence of these antibodies does not necessarily imply the development of thyroid dysfunction, as some individuals may have detectable antibodies without exhibiting clinical symptoms.
Children with positive thyroid antibodies and normal thyroid hormone levels may need periodic monitoring especially if the thyroid gland is enlarged. If thyroid levels are normal, your provider may recommend periodic screening with lab tests. The parent may need to be counseled on signs of hypothyroidism that may guide future screening.
Treatment Implications
You may wonder how this can be treated? Currently, there is no treatment to prevent or dampen the misfire of this immune response. Once the thyroid hormone production diminishes, as determined by blood tests, thyroid hormone replacement is initiated in cases of hypothyroidism associated with Hashimoto’s thyroiditis.
On the other hand, individuals with Graves’ disease who have elevated thyroid receptor antibodies may require a different approach, such as antithyroid medications, radioactive iodine therapy, or even surgical intervention to manage the hyperthyroidism.
Understanding Anti Thyroid Peroxidase Antibodies and Anti Thyroglobulin Antibodies
Understanding the differences between TPO Ab, AntiTg Ab, and thyroid receptor antibodies allows for improved diagnostic accuracy and tailored treatment approaches. Healthcare professionals can utilize the presence and levels of these antibodies to identify individuals at risk or already affected by autoimmune thyroid disorders, such as Hashimoto’s thyroiditis and Graves’ disease.
Dr. McIver is a board certified pediatrician and pediatric endocrinologist who specializes in treating hypothyroidism in children. To learn more about hypothyroidism and how to treat it, keep up with our blog!